Liquid crystal display

ABSTRACT

A liquid crystal display using a ferroelectric liquid crystal, which can give mono-domain alignment of the ferroelectric liquid crystal without forming alignment defects such as zigzag defects, hairpin defects and double domains and which is so remarkably good in alignment stability that the alignment thereof can be maintained even if the temperature of the liquid crystal is raised to the phase transition point or higher. The liquid crystal display has a ferroelectric liquid crystal sandwiched between two substrates, wherein an electrode and a photo alignment layer are each successively formed on opposite faces of the two substrates facing each other, and a constituent material of the respective photo alignment layer has a different composition with the ferroelectric liquid crystal sandwiched therebetween.

TECHNICAL FIELD

The present invention relates to a liquid crystal display usingferroelectric liquid crystal, more specifically, a liquid crystaldisplay in which a photo alignment layer is used to control thealignment of ferroelectric liquid crystal.

BACKGROUND ART

Since liquid crystal displays have features that it is thin and is lowin power consumption and other features, the use thereof has beenexpanding in various articles from large-sized displays to portableinformation terminals and the development thereof has been activelymade. Conventionally, for liquid crystal displays, a TN system, an STNmultiplex driving system, an active matrix driving system in which thinfilm transistors (TFTs) are used in TN, and others have been developedand made practicable. However, since nematic liquid crystal is usedtherein, the response speed of the liquid crystal material is as smallas several milliseconds to several tens of milliseconds and it cannot besaid that these sufficiently cope with display of moving images.

Ferroelectric liquid crystal (FLC) exhibits a very fast response inorder of microseconds, and thus FLC is a liquid crystal suitable forhigh-speed devices. About ferroelectric liquid crystal, there is wellknown a bistable liquid crystal which has two stable states when novoltage is applied thereto and is suggested by Clark and Lagerwall (FIG.1). However, the liquid crystal has a problem that the liquid crystalhas memory property but gray scale display cannot be attained since theswitching thereof is limited to two states, namely, bright and darkstates.

In recent years, attention has been paid to ferroelectric liquid crystalin which the liquid crystal layer thereof is stable in a single state(hereinafter referred to as “monostable”) when no voltage is appliedthereto as a liquid crystal which makes it possible to attain gray scaledisplay by the matter that the director (the inclination of the moleculeaxis) of the liquid crystal is continuously changed by a change inapplied voltage so as to analogue-modulate the light transmissionthereof (non-patent document 1, FIG. 1). As such liquid crystalexhibiting mono-stability, there is usually used a ferroelectric liquidcrystal in which phase change is caused between cholesteric phase (Ch)and chiral smectic C phase (SmC*) via no smectic A phase (SmA). Whenferroelectric liquid crystal exhibits mono-stability in this manner, theliquid crystal does not have any memory property and it is desired todrive the liquid crystal through an active matrix system in which anactive element such as a transistor or a diode is added to each pixel.In the case of using, in particular, an active matrix system using TFTelements as active elements, high-quality display can be attained sincetarget pixels can be certainly switched on and off.

On the other hand, ferroelectric liquid crystal has a higher order ofmolecules therein than nematic liquid crystal; therefore, the formerliquid crystal is not easily aligned so that defects called zigzagdefects or hairpin defects are easily generated. Such defects cause afall in contrast based on light leakage. In particular, ferroelectricliquid crystal undergoing phase transition via no SmA phase generatestwo domains different in the layer normal-line direction thereof(hereinafter referred to as “double domains”) (FIG. 2). The doubledomains give such display that black and white are reversed so as tocause a serious problem (FIG. 3). As the method for removing the doubledomains, known is an electric field induced technique (, which uses DCvoltage during cooling process) of heating a liquid crystal cell to atemperature not lower than the Ch phase thereof, and then cooling theliquid crystal cell slowly while applying a DC voltage thereto(non-patent document 2). This method has problems that the alignment ofthe liquid crystal is disturbed when the temperature thereof is againraised to a temperature not lower than the phase transition temperaturethereof and the alignment is disturbed in regions where no electricfield acts between pixel electrodes, and other problems.

As the technique for subjecting liquid crystal to alignment treatment,there is known a method of using an alignment film. The method isclassified into the rubbing method and the photo alignment method. Therubbing method is a method of subjecting a substrate coated with apolyimide film to rubbing treatment to align chains of the polyimidepolymer in the direction of the rubbing, thereby aligning liquid crystalmolecules on the film. The rubbing method is excellent incontrollability of the alignment of nematic liquid crystal, and isgenerally an industrially applicable technique. However, this method hasthe following problems: the generation of static electricity and dust,unevenness in the power for regulating the alignment and the tilt angleof liquid crystal caused by differences in rubbing conditions,treatment-ununiformity caused when a large area is treated, and so on.Thus, this method is unsuitable as a method for alignment treatment offerroelectric liquid crystal, in which alignment defects are easilygenerated. Moreover, the rubbing method cannot overcome double domains.

There is a photo alignment method as a non-contact alignment methodsubstituting the rubbing method. The photo alignment method is a methodof radiating light the polarization of which is controlled onto asubstrate coated with a polymer film or a monomolecular film to generatephoto-excited reaction (decomposition, isomerization or dimerization) soas to give anisotropy to the polymer film or a monomolecular film,thereby aligning the liquid crystal molecules on the film. This methodis useful since the generation of static electricity or dust, which is aproblem in the rubbing method, does not arise and the alignmenttreatment can be quantitatively controlled. However, even if this methodis used, it is difficult to suppress the generation of double domainsand obtain mono-domain alignment.

Another method for making ferroelectric liquid crystal monostable is thepolymer stabilization method. The polymer stabilization method is amethod of injecting a ferroelectric liquid crystal blended with anultraviolet curable monomer into a liquid crystal cell subjected toalignment treatment, and then radiating ultraviolet rays onto the liquidcrystal in the state that an AC or DC voltage is applied thereto,thereby polymerizing the monomer to stabilize the liquid crystal.However, the method has problems that the production process thereof iscomplicated and the voltage for driving the liquid crystal is high.

As still another method for giving mono-domains, the patent document 1describes a method of subjecting one out of alignment-films on andbeneath a ferroelectric liquid crystal to rubbing treatment, andsubjecting the other to photo alignment treatment, thereby aligning theferroelectric liquid crystal. However, according to this method, thereremain problems such as the generation of static electricity or dust andtreatment-ununiformity generated when a large area is treated, asdescribed above, since only one of the films is rubbed.

On the other hand, in recent years, color liquid crystal displays havebeen actively developed. The method for realizing color display isgenerally classified into a color filter system and a field sequentialcolor system. The color filter system is a system of using a white lightsource as a back light and attaching a micro color filter in R, G or Bcolor to each pixel, thereby realizing color display. On the other hand,the field sequential color system is a system of switching a back lightinto R, G, B, R, G, B . . . with time, and opening and shutting a blackand white shutter of a ferroelectric liquid crystal in synchronizationtherewith to mix the colors with time by after image effect on theretina, thereby realizing color display. This field sequential colorsystem makes it possible to attain color display in each pixel, and doesnot require any color filter low in transmission. As a result, thissystem is useful since the system is capable of attaining bright andhighly precise color display and realizing low power consumption and lowcosts. However, the field sequential color system is a system in whicheach pixel is subjected to time sharing; it is therefore necessary forthe liquid crystal as the black and white shutter to have high-speedresponsiveness in order to give a good moving image display property. Ifferroelectric liquid crystal is used, this problem can be solved.However, the ferroelectric liquid crystal has a problem that alignmentdefects are easily generated, as described above, and thus the colorsystem using this liquid crystal has not been made practicable.

-   Patent document 1: Japanese Patent Application Laid-Open No.    2003-5223-   Non-patent document 1: NONAKA, T., LI, J., OGAWA, A., HORNUNG, B.,    SCHMIDT, W., WINGEN, R., and DUBAL, H., 1999, Liq. Cryst., 26, 1599.-   Non-patent document 2: PATEL, J., and GOODBY, J. W., 1986, J. Appl.    Phys., 59, 2355

DISCLOSURE OF INVENTION

Problem to be Solved by the Invention

A main object of the present invention is to provide a liquid crystaldisplay using a ferroelectric liquid crystal, which can give mono-domainalignment of the ferroelectric liquid crystal without forming alignmentdefects such as double domains and which are so remarkably good inalignment stability that the alignment thereof can be maintained even ifthe temperature of the liquid crystal is raised to the phase transitionpoint or higher.

Means for Solving the Problem

In light of the above-mentioned situation, the inventors have made eagerinvestigation so as to find out that a photo alignment layer is formedon each of opposite faces of two substrates and materials havingdifferent compositions are used as the materials of the upper and lowerphoto alignment layers, whereby the mono-domain alignment of aferroelectric liquid crystal therebetween can be obtained in the statethat alignment defects such as double domains are restrained from beinggenerated. Thus, the present invention has been made.

That is, the present invention provides a liquid crystal displaycomprising a ferroelectric liquid crystal sandwiched between twosubstrates, wherein an electrode and a photo alignment layer are eachsuccessively formed on opposite faces of the two substrates facing eachother, and a constituent material of the respective photo alignmentlayer has a different composition with the ferroelectric liquid crystalsandwiched therebetween.

In the present invention, since a respective photo alignment layer isformed on the opposite faces of the upper and lower substrates facingwith each other, and the respective photo alignment layer is made ofmaterials of different compositions with the ferroelectric liquidcrystal sandwiched therebetween, the effect of aligning theferroelectric liquid crystal without formation of the alignment defectssuch as the double domain can be achieved. Since the present inventionis a liquid crystal display in which the photo alignment layers are usedto conduct alignment treatment without depending on the electric fieldinduced technique (which uses DC voltage during cooling process), theinvention has an advantage that even if the temperature thereof israised to the phase transition point thereof or higher, the alignment ofthe liquid crystal can be maintained so as to restrain alignment defectssuch as double domains from being generated.

It is preferable that each of the constituent materials of the photoalignment layers is a photo-isomerizable material comprising aphoto-isomerization-reactive compound which generates aphoto-isomerization reaction to give anisotropy to the respective photoalignment layer. By the use of the photo-isomerizable material, theanisotropy can be given easily to the photo alignment layers.

It is preferable that the photo-isomerization-reactive compound is acompound which has dichroism that different absorptivities are exhibiteddepending on a polarization direction thereof and further generates thephoto-isomerization reaction by a light irradiation. By generating theisomerization of the reactive site aligned in the polarization directionof the photo-isomerization-reactive compound having such properties,anisotropy can easily be given to the photo alignment layers.

In the photo-isomerization-reactive compound, it is preferable that thephoto-isomerization reaction is a cis-trans isomerization reaction. Thisis because any one of the isomers, a cis-isomer or a trans-isomer,increases by the light irradiation, whereby anisotropy can be given tothe photo alignment layers.

The photo-isomerization-reactive compound is preferably a compoundhaving, in a molecule thereof, an azobenzene skeleton for the followingreason: any azobenzene skeleton is subjected to the cis-transisomerization reaction by the irradiation thereof with light; therefore,when the compound having, in the molecule thereof, an azobenzeneskeleton is contained as the constituent material of the respectivephoto alignment layer, anisotropy can easily be given to the photoalignment layer. This is also for the following reason: when thecompound has the azobenzene skeleton, the anisotropy given to therespective photo alignment layer is particularly suitable forcontrolling the alignment of the ferroelectric liquid crystal.

The photo-isomerization-reactive compound is a polymerizable monomerhaving, as its side chain, an azobenzene skeleton. This is becauseanisotropy can easily be given to the respective photo alignment layerand the anisotropy can be made stable when the polymerizable monomerhaving, as its side chain, an azobenzene skeleton contained as theconstituent material of the photo alignment layer.

The ferroelectric liquid crystal is preferably a ferroelectric liquidcrystal that exhibits mono-stability. This is because the advantageouseffects resulting from the structure of the present invention becomesremarkable by using the ferroelectric liquid crystal which exhibitsmono-stability as the ferroelectric liquid crystal.

The ferroelectric liquid crystal is preferably a ferroelectric liquidcrystal having, in a phase series thereof, no smectic A phase. Asdescribed above, the ferroelectric liquid crystal having, in the phaseseries thereof, no smectic A phase easily generates alignment defectssuch as double domains. However, when the compositions of the upper andlower photo alignment layers, which sandwich the ferroelectric liquidcrystal, are made different from each other, alignment defects such asdouble domains can be restrained from being generated so that theadvantageous effects resulting from the structure of the presentinvention become remarkable.

The ferroelectric liquid crystal is preferably a ferroelectric liquidcrystal which constitutes a single phase. This is because the liquidcrystal display of the present invention provides the followingadvantages: a preferable alignment can be obtained even with a singlephase ferroelectric liquid crystal, without the need of using a methodsuch as a polymer stabilizing method for controlling the alignment, soas to facilitate the production process easily while lowering thedriving voltage.

The liquid crystal display is preferably driven by an active matrixsystem using a thin film transistor. This is because the adoption of theactive matrix system using TFT elements makes it possible to switch onor off target pixels surely to give high-quality display. Furthermore,it is possible to combine a TFT substrate, in which TFT elements arearranged in a matrix form on one of the substrates, with a commonelectrode substrate, in which a common electrode is formed in the wholeof the display section of the other substrate, to form a micro colorfilter in which TFT elements are arranged in a matrix form between thecommon electrode of the common electrode substrate and the substratethereof, and use the resultant as a color liquid crystal display.

Moreover, the liquid crystal display is preferably displayed by a fieldsequential color system for the following reason: the liquid crystaldisplay has fast switching speed and makes it possible to align theferroelectric liquid crystal therein without forming any alignmentdefect; therefore, when the display is displayed by the field sequentialcolor system, bright and highly precise display of color moving imageswhich has a wide view angle can be realized at low costs and low powerconsumption.

Effect of the Invention

The liquid crystal display of the invention is useful since the liquidcrystal display makes it possible to align the ferroelectric liquidcrystal therein without forming alignment defects such as zigzagdefects, hairpin defects or double domains, and further the liquidcrystal display is a liquid crystal display so remarkably good inalignment stability that the alignment is not easily disturbed even ifthe temperature thereof is raised to the phase transition point thereofor higher.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph showing changes in transmission as a function ofvoltage applied to ferroelectric liquid crystals.

FIG. 2 is a view illustrating a difference of alignment defects based ona difference of the phase series that ferroelectric liquid crystal has.

FIG. 3 is a photograph showing double domains which are alignmentdefects of ferroelectric liquid crystal.

FIG. 4 is a schematic perspective view illustrating one example of theliquid crystal display of the present invention.

FIG. 5 is a schematic sectional view illustrating one example of theliquid crystal display of the present invention.

EXPLANATION OF REFERENCES

-   1 . . . liquid crystal layer-   2 a, 2 b . . . photo alignment layer-   3 a . . . common electrode-   3 b . . . x electrode-   3 c . . . y electrode-   3 d . . . pixel electrode-   4 a, 4 b . . . substrate-   5 a, 5 b . . . polarizing plate-   7 . . . TFT element

BEST MODE FOR CARRYING OUT THE INVENTION

The liquid crystal display of the present invention will be described indetail hereinafter. The liquid crystal display of the invention is aliquid crystal display comprising a ferroelectric liquid crystalsandwiched between two substrates in which an electrode and a photoalignment layer are successively formed on each of opposite faces of thetwo substrates, and the constituent material of the respective photoalignment layer has a composition different from each other so as tosandwich the ferroelectric liquid crystal.

The liquid crystal display of the invention will be described withreference to the drawings. FIG. 4 is a schematic perspective viewillustrating one example of the liquid crystal display of the presentinvention, and FIG. 5 is a schematic sectional view thereof. As shown inFIGS. 4 and 5, a common electrode 3 a is formed on a substrate 4 a, andx electrodes 3 b, y electrodes 3 c and pixel electrodes 3 d are formedon an opposite substrate 4 b. Inside an electrode layer that theseelectrodes constitute are formed photo alignment layers 2 a and 2 b. Aferroelectric liquid crystal is sandwiched between the photo alignmentlayers 2 a and 2 b to constitute a liquid crystal layer 1. In FIG. 4,the illustration of photo alignment layers 2 a and 2 b is omitted.

Polarizing plates 5 a and 5 b may be formed outside of the substrates 4a and 4 b. This makes it possible to convert incident light into linearpolarized light so that the liquid crystal display can transmit onlylight polarized in the alignment direction of the liquid crystalmolecules. The polarizing plates 5 a and 5 b are arranged in such amanner that the polarization direction thereof is twisted at 90°. Thismakes it possible to control the direction of the optical axis of theliquid crystal molecules or the magnitude of the birefringence of theliquid crystal molecules between states that voltage is not appliedthereto and is applied thereto, and to produce a bright state and a darkstate by use of the ferroelectric liquid crystal molecules as a blackand white shutter. For example, in the state that no voltage is applied,the light transmitted through the polarizing plate 5 a cannot be causedto rotate its polarization direction at an angle of 90° by setting thepolarizing plate 5 a to make consistent with the alignment of the liquidcrystal molecules. Consequently, this light is blocked by the polarizingplate 5 b so that the liquid crystal is turned into a dark state. On theother hand, in the state that voltage is applied, the direction of theliquid crystal molecules are changed by the voltage so that the opticalaxis thereof rotates by an angle of θ from the initial state, wherebythe polarization direction of the light is twisted at 90°. As a result,the light is transmitted through the polarizing plate 5 b so that theliquid crystal is turned into a bright state. When the quantity of thetransmitted light is controlled in accordance with the applied voltage,gray scale display can be attained.

The liquid crystal display of the invention has a photo alignment layeron each of opposite faces of upper and lower substrates and the photoalignment layers are made of materials different from each other tosandwich a ferroelectric liquid crystal as described above, therebymaking it possible to restrain the generation of alignment defects suchas zigzag defects, hairpin defects and double domains and yield themono-domain alignment of the ferroelectric liquid crystal. The presentinvention causes the ferroelectric liquid crystal to be aligned withoutusing the electric field induced technique (which uses DC voltage duringcooling process); therefore, the invention has advantages that alignmentdisturbance, which is based on a rise in the temperature of the liquidcrystal up to not lower than the phase transition point thereof and is aproblem of the electric field induced technique, is not easily generatedso that the invention is excellent in alignment stability. The reasonwhy the use of materials different in composition, as the constituentmaterials of the photo alignment layers, gives a good alignment state isunclear, but would be based on the difference of the interaction betweenthe upper photo alignment layer and the ferroelectric liquid crystal andbetween the lower photo alignment layer and the ferroelectric liquidcrystal. Since a ferroelectric liquid crystal is used as a black andwhite shutter in the liquid crystal display of the invention asdescribed above, the liquid crystal display has an advantage that theresponse speed thereof can be made large.

As shown in, for example, FIG. 4, the liquid crystal display of thepresent invention is preferably a display in which one of the substratesis rendered a TFT substrate in which thin film transistors (TFTs) 7 arearranged in a matrix form, the other substrate is rendered a commonelectrode substrate having the common electrode 3 a formed on the wholearea thereof, and the two substrates are combined with each other. Suchliquid crystal display of an active matrix system using TFT elementswill be described hereinafter.

In FIG. 4, in one of the substrates, its electrode is the commonelectrode 3 a, and thus the substrate is a common electrode substrate.On the other hand, in the opposite substrate, its electrodes arecomposed of the x electrodes 3 b, the y electrodes 3 c and the pixelelectrodes 3 d, and thus the substrate is a TFT substrate. In thisliquid crystal display, the electrodes 3 b and the y electrodes 3 c arearranged lengthwise and crosswise, respectively. When signals are addedto these electrodes, the TFT elements 7 are worked so as to drive theferroelectric liquid crystal. Regions where the x electrodes 3 b and they electrodes 3 c cross are insulated with an insulator layer, which isnot illustrated. Signals to the x electrodes 3 b and signals to the yelectrodes 3 c can be independently operated. Any region surrounded bythe x electrodes 3 b and the y electrodes 3 c is a pixel, which is aminimum unit for driving the liquid crystal display of the invention. Atleast one out of the TFT elements 7 and at least one out of the pixelelectrodes 3 d are fitted to each of the pixels. In the liquid crystaldisplay of the invention, the TFT elements 7 of the respective pixelscan be worked by applying signal voltages successively to the xelectrodes 3 b and the y electrodes 3 c.

Furthermore, the liquid crystal display of the invention can be used ascolor liquid crystal displays by forming a micro color filter in whichTFT elements 7 are arranged in a matrix form between the commonelectrode 3 a and the substrate 4 a. Each of the constituent members ofthe liquid crystal display of the invention, as described above, will bedescribed in detail hereinafter.

1. Constituent Members of Liquid Crystal Display

(1) Photo Alignment Layer

The photo alignment layer is a film, wherein light the polarization ofwhich is controlled is radiated onto a substrate coated with aconstituent material of the photo alignment layer, to be describedlater, to generate photo-excited reaction (decomposition, isomerizationor dimerization), thereby giving anisotropy into the obtained film toalign liquid crystal molecules on this film.

The constituent material of the photo alignment layer used in theinvention is not limited to any especial kind if the material has aneffect of generating photo-excited reaction by the irradiation thereofwith light to align the ferroelectric liquid crystal thereon(photoaligning). Such a material can be roughly classified into aphoto-isomerizable type, in which only the shape of the molecule thereofchanges so that the alignment there of can reversibly change, and aphotoreactive type, in which the molecule itself changes. Among them, inthe present invention, a photo-isomerizable material comprising aphoto-isomerization-reactive compound which generates aphoto-isomerization reaction to give anisotropy to the photo alignmentlayer is preferable. Here, the photo-isomerization reaction means aphenomenon that a single compound is changed into some other isomer bythe irradiation thereof with light. The use of such aphoto-isomerizable-reactive material makes it possible to increase astable isomer from plural isomers by the irradiation with light, wherebyanisotropy can easily be given to the photo alignment layer.

The wavelength range of light which causes photo-excited reaction in theconstituent material of the photo alignment layer is preferably withinthe wavelength range of ultraviolet rays, that is, the range of 10 to400 nm, more preferably within the range of 250 to 380 nm.

The photo-isomerization-reactive compound is not limited to any especialkind if the compound is a material capable of giving anisotropy to thephoto alignment layer by photo-isomerization reaction, and is preferablya compound which has dichroism that different absorptivities areexhibited depending on the polarization direction thereof and generatesphoto-isomerization reaction by the light irradiation. By generating theisomerization of the reactive site aligned in the polarization directionof the photo-isomerization-reactive compound having such properties,anisotropy can easily be given to the photo alignment layer.

For the photo-isomerization-reactive compound, the photo-isomerizationreaction is preferably the cis-trans isomerization reaction. This isbecause anyone of the isomers, a cis-isomer or a trans-isomer, increasesby the light irradiation, whereby anisotropy can be given to the photoalignment layer.

Examples of the photo-isomerization-reactive compound used in thepresent invention may be monomolecular compounds or polymerizablemonomers polymerizable with light or heat. These should be appropriatelyselected in accordance with the kind of the used ferroelectric liquidcrystal. It is preferable to use any one of the polymerizable monomerssince the monomer gives anisotropy to the photo alignment layer by thelight irradiation and subsequently the monomer is polymerized, wherebythe anisotropy can be made stable. Of such polymerizable monomers,preferable is an acrylate monomer or methacrylate monomer since themonomer gives anisotropy to the photo alignment layer and subsequentlythe monomer can easily be polymerized in the state that the anisotropyis kept good.

The polymerizable monomer may be a monofunctional monomer or apolyfunctional monomer. A bifunctional monomer is preferable since theanisotropy of the photo alignment layer, based on the polymerization,becomes more stable.

Specific examples of such a photo-isomerization-reactive compoundinclude compounds having a cis-trans isomerization-reactive skeleton,such as an azobenzene skeleton or a stilbene skeleton.

In this case, the number of the cis-trans isomerization-reactiveskeleton(s) in the molecule may be one or more, and is preferably twosince the alignment of the ferroelectric liquid crystal is easilycontrolled.

The cis-trans isomerization-reactive skeleton(s) may have a substituentin order to make interaction thereof with the liquid crystal moleculeshigher. The substituent is not limited to any especial kind if thesubstituent can make the interaction with the liquid crystal moleculeshigh and further does not hinder the alignment of the cis-transisomerization-reactive skeleton(s). Examples thereof include a carboxylgroup, a sodium sulfonate group, and a hydroxyl group. These skeletonstructures can be appropriately selected in accordance with the kind ofthe used ferroelectric liquid crystal.

The photo-isomerization-reactive compound may have a group containingmany π electrons in the molecule, such as an aromatic hydrocarbon group,besides the cis-trans isomerization-reactive skeleton in order to makethe interaction with the liquid crystal molecules higher. The cis-transisomerization-reactive skeleton and the aromatic hydrocarbon group maybe bonded to each other through a bonding group. The bonding group isnot limited to any especial kind if the group can make the interactionwith the liquid crystal molecules high. Examples thereof include —COO—,—OCO—, —O—, —C≡C—, —CH₂—CH₂—, —CH₂O—, and —OCH₂—.

In the case of using a polymerizable monomer as thephoto-isomerization-reactive compound, it is preferable that the monomerhas, as its side chain, the above-mentioned cis-transisomerization-reactive skeleton. When the monomer has, as its sidechain, the cis-trans isomerization-reactive skeleton, the advantageouseffect of the anisotropy given to the photo alignment layer becomeslarger and this compound becomes particularly suitable for the controlof the alignment of the ferroelectric liquid crystal. In this case, itis preferable that the above-mentioned aromatic hydrocarbon group andthe bonding group contained in the molecule are contained, together withthe cis-trans isomerization-reactive skeleton, in the side chain so asto make the interaction with the liquid crystal molecules high.

The side chain of the polymerizable monomer may have, as a spacer, analiphatic hydrocarbon group such as an alkylene group so that thecis-trans isomerization-reactive skeleton can easily be aligned.

Of the above-mentioned photo-isomerization-reactive compounds ofmonomolecular compounds or polymerizable monomers as described above,any compound having in the molecule thereof an azobenzene skeleton ispreferable as the photo-isomerization-reactive compound used in thepresent invention. This is because the azobenzene skeleton interactshighly with the liquid crystal molecules and is particularly suitablefor the control of the alignment of the ferroelectric liquid crystalsince the skeleton contains many π electrons.

when the azobenzene skeleton is irradiated with linearly polarizedultraviolet rays, the azobenzene skeleton of a trans isomer, as shown inthe below formula (1), in which its molecule long axis is aligned in thepolarization direction, is changed to the cis isomer thereof.

Since the cis isomer of the azobenzene skeleton is more chemicallyunstable than trans isomers thereof, the cis isomer returns thermally toany one of the trans isomers or absorbs visible rays to returns thereto.At this time, it happens with the same possibility whether the cisisomer turns to the trans isomer at the left side or the trans isomer atthe right side in above formula (1). Accordingly, when the azobenzeneskeleton continues to absorb ultraviolet rays, the ratio of the transisomer at the right side increases so that the average alignmentdirection of the azobenzene skeleton becomes perpendicular to thepolarized direction of ultraviolet ray. In the present invention, thisphenomenon is used to make alignment directions of skeletons ofazobenzene consistent with each other, thereby giving anisotropy to thephoto alignment layer to control the alignment of liquid crystalmolecules on the film.

An example of a monomolecular compound out of the compounds each havingin the molecule thereof an azobenzene skeleton used in the presentinvention may be a compound represented by the following formula.

In the above formula, R²¹s each independently represent a hydroxy group.R²² represents a linking group represented by-(A²¹-B²¹-A²¹)_(m)-(D²¹)_(n)- and R²³ represents a linking grouprepresented by (D²¹)_(n)-(A²¹-B²¹-A²¹)_(m)-, wherein A²¹ represents abivalent hydrocarbon group, B²¹ represents —O—, —COO—, —OCO—, —CONH—,—NHCO—, —NHCOO—or —OCONH—, m represents an integer of 0 to 3, D²¹represents a bivalent hydrocarbon group when m is 0 and represents —O—,—COO—, —OCO—, —CONH—, —NHCO—, —NHCOO— or —OCONH— when m is an integer of1 to 3, and n represents 0 or 1. R²⁴s each independently represent ahalogen atom, a carboxy group, a halogenated methyl group, a halogenatedmethoxy group, a cyano group, a nitro group, a methoxy group, or amethoxycarbonyl group provided that the carboxy group may be combinedwith an alkali metal to form a salt. R²⁵s each independently represent acarboxy group, a sulfo group, a nitro group, an amino group or a hydroxygroup provided that the carboxy group or the sulfo group may be combinedwith an alkali metal to form a salt.

Specific examples of the compound represented by the above-mentionedformula include the following compounds.

An example of the polymerizable monomer having in its side chain anazobenzene skeleton used in the present invention may be a compoundrepresented by the following formula.

In the above formula, R³¹s each independently represent a(meth)acryloyloxy group, a (meth)acrylamide group, a vinyloxy group, avinyloxycarbonyl group, a vinyliminocarbonyl group, avinyliminocarbonyloxy group, a vinyl group, an isopropenyloxy group, anisopropenyloxycarbonyl group, an isopropenyliminocarbonyl group, anisopropenyliminocarbonyloxy group, an isopropenyl group or an epoxygroup; R³² represents a linking group represented by-(A³¹-B³¹-A³¹)_(m)-(D³¹)_(n)- and R³³ represents a linking grouprepresented by (D³¹)_(n)-(A³¹-B³¹-A³¹)_(m)- wherein A³¹ represents abivalent hydrocarbon group, B³¹ represents —O—, —COO—, —OCO—, —CONH—,—NHCO—, —NHCOO— or —OCONH—, m represents an integer of 0 to 3, D³¹represents a bivalent hydrocarbon group when m is 0 and represents —O—,—COO—, —OCO—, —CONH—, —NHCO—, —NHCOO— or —OCONH— when m is an integer of1 to 3, and n represents 0 or 1. R³⁴s each independently represent ahalogen atom, a carboxy group, a halogenated methyl group, a halogenatedmethoxy group, a cyano group, a nitro group, a methoxy group, or amethoxycarbonyl group provided that the carboxy group may be combinedwith an alkali metal to form a salt. R³⁵s each independently represent acarboxy group, a sulfo group, a nitro group, an amino group or a hydroxygroup provided that the carboxy group or the sulfo group may be combinedwith an alkali metal to form a salt.

A specific example of the compound represented by the above-mentionedformula is the following compound.

In the present invention, the compositions of the upper and lower photoalignment layers can be made different by variously selecting thecis-trans isomerization reactive compound or the substituent accordingto the required characteristics out of the photo-isomerization-reactivecompounds. In this case, as the photo-isomerization-reactive compoundsused for the upper and lower photo alignment layers, those having thesame cis-trans isomerization reactive skeletons or those havingdifferent ones can be used as well. Moreover, two or more kinds of thephoto-isomerization-reactive compounds can be used in a combination sothat the compositions of the upper and lower photo alignment layers canbe changed by changing the combination or changing the compositionratios of the same combination.

Additives, besides the above-mentioned photo-isomerization-reactivecompound, may be contained as constituent materials of the photoalignment layer used in the present invention as long as thephotoaligning of the photo alignment layer is not hindered. In the caseof using a polymerizable monomer as the photo-isomerization-reactivecompound, examples of the additives include a polymerization initiatorand a polymerization inhibitor.

It is advisable to select the polymerization initiator or thepolymerization inhibitor appropriately from generally-known compounds inaccordance with the kind of the photo-isomerization-reactive compoundand then use the selected one. The added amount of the polymerizationinitiator or the polymerization inhibitor is preferably from 0.001 to20% by weight, more preferably from 0.1 to 5% by weight of thephoto-isomerization-reactive compound. If the added amount of thepolymerization initiator or the polymerization inhibitor is too small,the polymerization may not be initiated (or inhibited). Conversely, ifthe amount is too large, the reaction may be hindered.

As mentioned above, in the present invention, the constituent materialsfor the photo alignment layer 2 a and the photo alignment layer 2 b havedifferent compositions. In the present invention, the compositions ofthe upper and lower photo alignment layers can be made different byvariously selecting the cis-trans isomerization reactive skeleton or thesubstituent from the photo-isomerization-reactive compound according tothe required characteristics, and the compositions can be changed bychanging the addition amount of the additives as well.

The following will describe the photo alignment treatment method. First,the face of an electrode-formed substrate which is to oppose to a liquidcrystal layer is coated with a coating solution in which theabove-mentioned constituent material of the photo alignment layer isdiluted with an organic solvent, and then the solution is dried. In thiscase, the content of the photo-isomerization-reactive compound in thecoating solution is preferably from 0.05 to 10% by weight, morepreferably from 0.2 to 5% by weight. If the content ofphoto-isomerization-reactive compound is too small, an appropriateanisotropy is not easily given to the photo alignment layer. Conversely,if the content is too large, the viscosity of the coating solutionbecomes so high that a homogeneous coat film is not easily formed.

The coating method which can be used is spin coating, roll coating, rodbar coating, spray coating, air knife coating, slot die coating, wirebar coating or the like.

The thickness of the film obtained by the coating with the constituentmaterial is preferably from 1 to 200 nm, more preferably from 3 to 100nm. If the thickness of the film is too small, a sufficientphotoaligning may not be obtained. Conversely, if the thickness is toolarge, the alignment of the liquid crystal molecules may be disturbedand further, costs therefor are not preferred.

The resultant film causes photo-excited reaction by the irradiationthereof with light the polarization of which is controlled, wherebyanisotropy can be given. The wavelength range of the radiated lightshould be appropriately selected in accordance with the constituentmaterial of the used photo alignment layer. It is preferably the rangeof ultraviolet ray wavelengths, that is, the range of 100 to 400 nm,more preferably the range of 250 to 380 nm.

Moreover, the photo alignment treatment of the film can also beconducted by radiating oblique non-polarized ultraviolet rays. Thedirection of the light is not especially limited if the direction makesit possible to generate the photo-excited reaction. It is preferably inthe range of 0° to 45° oblique to the substrate face of the upper andlower photo alignment layers, more preferably in the range of 30° to 45°oblique thereto since the alignment state of the ferroelectric liquidcrystal can be made good.

In the case of using a polymerizable monomer as described above as thephoto-isomerization-reactive compound used in the invention, the photoalignment treatment is conducted, and then the monomer is heated,thereby polymerizing the monomer. In this way, the anisotropy given tothe photo alignment layer can be made stable.

(2) Liquid Crystal Layer

The liquid crystal layer used in the invention is made by sandwiching aferroelectric liquid crystal between the photo alignment layers. Theferroelectric liquid crystal used in the liquid crystal layer is notlimited to any especial kind if the ferroelectric liquid crystalexhibits a chiral smectic C phase (SmC*). The liquid crystal ispreferably a ferroelectric liquid crystal material the phase series ofwhich is a phase change from a cholesteric phase (Ch) to a chiralsmectic C phase (SmC*) via no smectic A phase (SmA).

The liquid crystal display of the present invention is preferably drivenby an active matrix system using thin film transistors (TFTs), and canbe rendered a color liquid crystal display by adopting a color filtersystem or a field sequential color system. In such a case, a materialthe phase of which changes from a Ch phase through a SmA phase to a SmC*phase can be used as the ferroelectric liquid crystal. Alternatively, amaterial the phase of which changes from a Ch phase to a SmC* phase viano SmA phase may be used. However, in the case of driving the liquidcrystal display of the invention, in particular, by a field sequentialcolor system, it is preferable to use a liquid crystal material havingmono-stability and undergoing phase transition via no SmA phase. Themono-stability herein means a nature that liquid crystal has only onestable state when no voltage is applied thereto, as described above.Particularly preferable is a ferroelectric liquid crystal undergoinghalf-V-shaped driving, in which liquid crystal molecules thereof workonly when either one of positive or negative voltages is applied theretosince the liquid crystal makes it possible to lengthen the aperture timeof a black and white shutter and realize bright color display.

The ferroelectric liquid crystal used in the invention is preferably oneconstituting a single phase. The word “constituting a single phase”means that a polymer network, as formed by the polymer stabilizationmethod or the like, is not formed. Such use of the ferroelectric liquidcrystal of a single phase produces an advantage that the productionprocess becomes simple and the driving voltage can be made low.

The ferroelectric liquid crystal used in the invention may be, forexample, “R2301” sold by Clariant (Japan)K.K.

The thickness of the liquid crystal layer made of the above-mentionedferroelectric liquid crystal is preferably from 1.2 to 3.0 μm; morepreferably from 1.3 to 2.5 μm; and even more preferably from 1.4 to 2.0μn. If the thickness of the liquid crystal layer is too small, thecontrast may lower. Conversely, if the thickness is too large, theliquid crystal may not be aligned with ease.

As the method for forming the liquid crystal layer, method which isgenerally used as a method for forming a liquid crystal cell can beused. For example, the liquid crystal layer can be formed, by making useof capillary effect to inject an isotropic liquid obtained by heatingthe above-mentioned ferroelectric liquid crystal into a liquid crystalcell, which is formed by forming electrodes beforehand on a substrateand arranging the above-mentioned photo alignment layer, and thensealing the cell with an adhesive agent. The thickness of the liquidcrystal layer can be adjusted with spacers such as beads.

(3) Substrate

The substrate used in the invention is not limited to any especial kindif the substrate can be generally used as a substrate of liquid crystaldisplays. Preferred examples thereof include glass plates and plasticplates. The surface roughness (RSM value) of the substrate is preferably10 nm or less; more preferably 3 nm or less; and even more preferably 1nm or less. The surface roughness in the invention can be measured withan atomic force microscope (AFM).

(4) Electrodes

The electrodes used in the invention are not limited to any especialkind if the electrodes are electrodes which are generally used aselectrodes of liquid crystal displays. At least one of the electrodes ispreferably an electrode made of a transparent conductor. Preferredexamples of the material of the transparent conductor include an indiumoxide, a tin oxide, and an indium tin oxide (ITO). In the case ofrendering the liquid crystal display of the invention a liquid crystaldisplay of an active matrix system using TFT, one of upper and lowerelectrodes is rendered a full-face common electrode made of thetransparent conductor and the other is rendered an electrode in which xelectrodes and y electrodes are arranged in a matrix form and a TFTelement and a pixel electrode are arranged in a region surrounded byeach of the x electrodes and each of the y electrodes. In this case, thedifference between concave and convex portions of an electrode layermade of the pixel electrodes, the TFT elements, the x electrodes and they electrodes is preferably 0.2 μm or less. If the difference between theconcave and convex portions of the electrode layer is over 0.2 μm,alignment disturbance is easily generated.

About the above-mentioned electrodes, a transparent electroconductivefilm can be formed on the above-mentioned substrate by a vapordeposition method such as CVD, sputtering, or ion plating, and then thisis patterned into a matrix form, whereby the x electrodes and the yelectrodes can be obtained.

(5) Polarizing Plate

The polarizing plate used in the invention is not limited to anyespecial kind if the plate is a member for transmitting only a specificdirection of wave motions of light. It is possible to use a member whichis generally used as a polarizing plate for liquid crystal displays.

2. Process for Producing Liquid Crystal Display

The liquid crystal display of the invention can be produced by a processthat is generally used as a process for producing liquid crystaldisplays. The following will describe a process for producing liquidcrystal display of an active matrix system using TFT elements as oneexample of the process for producing a liquid crystal display of theinvention. A transparent electroconductive film is first formed on asubstrate by the above-mentioned vapor deposition method, so as to forma full-face common electrode. A transparent electroconductive film ispatterned into a matrix form on the other substrate to form x and yelectrodes, and switching elements and pixel electrodes are set up.

Next, the two substrates, on which the electrodes are formed, are coatedwith photo alignment layer materials having different compositions,respectively, and then subjected to photo alignment treatment to formphoto alignment layers. Beads are dispersed, as spacers, onto one of thethus-formed photo alignment layers, and a sealing agent is applied tothe periphery thereof. The two substrates are stuck onto each other soas to make the photo alignment layers opposite to each other. Thesubstrates are then thermally compressed. Capillary effect is used toinject a ferroelectric liquid crystal, in an isotropic liquid state,from an injecting port thereinto, and then the injecting port is sealedwith an ultraviolet curing resin or the like. Thereafter, theferroelectric liquid crystal is slowly cooled, whereby the liquidcrystal can be aligned. Polarizing plates are stuck onto the upper andthe lower of the thus-obtained liquid crystal cell, whereby liquidcrystal display of the present invention can be yield.

3. Usage of Liquid Crystal Display

The liquid crystal display of the present invention can be used as acolor liquid crystal display by adopting a color filter system or afield sequential color system. Since the color liquid crystal displayusing the liquid crystal display of the invention makes it possible toalign ferroelectric liquid crystal without generating alignment defectssuch as double domains, it is possible to realize highly precise colordisplay having a wide field angle and high-speed responsibility.

It is preferred to display the liquid crystal display of the inventionby the field sequential color system out of these for the followingreason. As described above, the field sequential color system is asystem in which each pixel is subjected to time sharing, and thushigh-speed responsibility is particularly necessary in order to obtain agood moving image display characteristic.

In this case, it is preferred to use a liquid crystal material havingmono-stability, in which a SmC* phase is exhibited from a Ch phase viano SmA phase, and it is particularly preferred to use a materialundergoing half-V-shaped driving, in which liquid crystal moleculesthereof work only when either one of positive or negative voltages isapplied thereto. When such a material undergoing half-V-shaped drivingis used, it is possible to make light leakage less when dark regionsoperate (when a black and white shutter is closed), and make theaperture time of the black and white shutter sufficiently long. Thismakes it possible to display respective colors switched with time morebrightly to realize a bright color liquid crystal display.

The present invention is not limited to the above-mentioned embodiments.The embodiments are examples, and all modifications having substantiallythe same structure and producing the same effects and advantages as thetechnical concept recited in the claims of the present invention areincluded in the technical scope of the invention.

EXAMPLES

The present invention will be described in more detail by way of thefollowing examples. Compounds 1 to 6 represented by the followingformulae were used as photo-isomerization-reactive compounds.

Example 1

Two glass substrates each coated with ITO were spin-coated with a 1% byweight solution of the compound 1 dissolved in N-methyl-2-pyrrolidinoneand 2-n-butoxyethanol (50:50% by weight) and a 1% by weight solution ofthe compound 5 dissolved in N-methyl-2-pyrrolidinone and2-n-butoxyethanol (50:50% by weight) at a rotation frequency of 4000 rpmfor 30 seconds. The substrate spin-coated with the solution of thecompound was dried at 100° C. in an oven for 1 minute, and thenpolarized ultraviolet rays were radiated onto the substrate at 1000mJ/cm² and at 25° C. Furthermore, the one having the solution of thecompound 5 spin-coated was heated at 150° C. under the atmosphere ofnitrogen for 1 hour after the exposure. Spacers of 1.5 μm size weresprayed onto one of the substrates, and a sealing material was appliedonto the other substrate with a seal disperser. Thereafter, thesubstrates were fabricated in parallel to the radiation direction of thepolarized ultraviolet rays and in an anti-parallel state, and thenthermally compressed. As the liquid crystal, the “2301” (manufactured byClariant (Japan) K.K.) was used. The liquid crystal was attached to theupper of an injecting port thereof, and an oven was used to perform theinjection of the liquid crystal at a temperature higher by 10° C. to 20°C. than the phase transition temperature between nematic and isotropicphases. The temperature was slowly returned to room temperature so thata mono-domain phase having no alignment defects was obtained.

Comparative Example 1

Two glass substrates each coated with ITO were spin-coated with a 1% byweight solution of the compound 1 dissolved in N-methyl-2-pyrrolidinoneand 2-n-butoxyethanol (50:50% by weight), at a rotation frequency of4000 rpm for 30 seconds. Thereafter, they were dried and subjected toexposure treatment in the same manner as in Example 1, thereafter, theresultant was heated at 150° C. under the atmosphere of nitrogen for 1hour. Furthermore, they were fabricated into a cell by theabove-mentioned method, and then the liquid crystal was injectedthereinto. As a result, no mono-domain phase was obtained, and alignmentdefects such as double domains, zigzag defects and hairpin defects weregenerated.

Comparative example 2

Two glass substrates each coated with ITO were spin-coated with a 1% byweight solution of the compound 5 dissolved in N-methyl-2-pyrrolidinoneand 2-n-butoxyethanol (50:50% by weight), at a rotation frequency of4000 rpm for 30 seconds. Thereafter, they were dried and subjected toexposure treatment in the same manner as in Example 1, thereafter, theresultant was heated at 150° C. under the atmosphere of nitrogen for 1hour. Furthermore, they were fabricated into a cell by theabove-mentioned method, and then the liquid crystal was injectedthereinto. As a result, no mono-domain phase was obtained, and alignmentdefects such as double domains, zigzag defects and hairpin defects weregenerated.

Example 2

In the same manner as in Example 1 except that the compound 2 was usedinstead of the compound 1 in Example 1, a mono-domain phase without analignment defect was obtained.

Example 3

Two glass substrates each coated with ITO were spin-coated with a 1% byweight solution of the compound 3 dissolved in N-methyl-2-pyrrolidinoneand 2-n-butoxyethanol (50:50% by weight) and a 1% by weight solution ofthe compound 5 dissolved in N-methyl-2-pyrrolidinone and2-n-butoxyethanol (50:50% by weight) at a rotation frequency of 4000 rpmfor 30 seconds. The substrate spin-coated with the solution of thecompound was dried at 100° C. in an oven for 1 minute, and thenpolarized ultraviolet rays were radiated onto the substrate at 1000mJ/cm² and at 25° C. Furthermore, after exposure, the resultant washeated at 150° C. under the atmosphere of nitrogen for 1 hour. Spacersof 1.5 μm size were sprayed onto one of the substrates, and a sealingmaterial was applied onto the other substrate with a seal disperser.Thereafter, the substrates were fabricated in parallel to the radiationdirection of the polarized ultraviolet rays and in an anti-parallelstate, and then thermally compressed. As the liquid crystal, the “2301”(manufactured by Clariant (Japan) K.K.) was used. The liquid crystal wasattached to the upper of an injecting port thereof, and an oven was usedto perform the injection of the liquid crystal at a temperature higherby 10° C. to 20° C. than the phase transition temperature betweennematic and isotropic phases. The temperature was slowly returned toroom temperature so that a mono-domain phase having no alignment defectswas obtained.

Example 4

In the same manner as in Example 1 except that the compound 4 was usedinstead of the compound 3 in Example 3, a mono-domain phase without analignment defect was obtained.

Example 5

In the same manner as in Example 1 except that the compound 3 was usedinstead of the compound 5 in Example 1, a mono-domain phase without analignment defect was obtained.

Example 6

In the same manner as in Example 1 except that the compound 4 was usedinstead of the compound 5 in Example 1, a mono-domain phase without analignment defect was obtained.

Example 7

Two glass substrates each coated with ITO were spin-coated with a 1% byweight solution of the compound 5 dissolved in N-methyl-2-pyrrolidinoneand 2-n-butoxyethanol (50:50% by weight) and a 1% by weight solution ofthe compound 6 dissolved in N-methyl-2-pyrrolidinone and2-n-butoxyethanol (50:50% by weight) at a rotation frequency of 4000 rpmfor 30 seconds. The substrate spin-coated with the solution of thecompound was dried at 100° C. in an oven for 1 minute, and thenpolarized ultraviolet rays were radiated onto the substrate at 1000mJ/cm² and at 25° C. Furthermore, the one having the solution of thecompound 5 spin-coated was heated at 150° C. under the atmosphere ofnitrogen for 1 hour after the exposure. Spacers of 1.5 μm size weresprayed onto one of the substrates, and a sealing material was appliedonto the other substrate with a seal disperser. Thereafter, thesubstrates were fabricated in parallel to the radiation direction of thepolarized ultraviolet rays and in an anti-parallel state, and thenthermally compressed. As the liquid crystal, the “2301” (manufactured byClariant (Japan) K.K.) was used. The liquid crystal was attached to theupper of an injecting port thereof, and an oven was used to perform theinjection of the liquid crystal at a temperature higher by 10° C. to 20°C. than the phase transition temperature between nematic and isotropicphases. The temperature was slowly returned to room temperature so thata mono-domain phase having no alignment defects was obtained.

1. A liquid crystal display comprising a ferroelectric liquid crystallayer sandwiched between two substrates, wherein an electrode and aphoto alignment layer are each successively formed on opposite faces ofthe two substrates facing each other; wherein a constituent material ofeach photo alignment layer is a photo-isomerizable material comprising aphoto-isomerization-reactive compound which generates aphoto-isomerization reaction to give anisotropy to the respective photoalignment layer, and the constituent material of the respective photoalignment layers have a different composition from each other, andwherein a ferroelectric liquid crystal in the ferroelectric liquidcrystal layer is a liquid crystal: having no smectic A phase in a phaseseries thereof, exhibiting mono-stability and undergoing half-V-shapeddriving; and further wherein the ferroelectric liquid crystal formsmono-domain alignment in the ferroelectric liquid crystal layer.
 2. Theliquid crystal display according to claim 1, wherein thephoto-isomerization-reactive compound is a compound which has dichroismthat different absorptivities are exhibited depending on a polarizationdirection thereof and further generates the photo-isomerization reactionby a light irradiation.
 3. The liquid crystal display according to claim2, wherein the photo-isomerization reaction is a cis-trans isomerizationreaction.
 4. The liquid crystal display according to claim 1, whereinthe photo-isomerization reaction is a cis-trans isomerization reaction.5. The liquid crystal display according to claim 1, wherein thephoto-isomerization-reactive compound is a compound having, in amolecule thereof, an azobenzene skeleton.
 6. The liquid crystal displayaccording to claim 1, wherein the photo-isomerization-reactive compoundis a polymerizable monomer having, as its side chain, an azobenzeneskeleton.
 7. The liquid crystal display according to claim 1, whereinthe ferroelectric liquid crystal is a liquid crystal which constitutes asingle phase.
 8. The liquid crystal display according to claim 1,wherein the liquid crystal display is driven by an active matrix systemusing a thin film transistor.
 9. The liquid crystal display according toclaim 1, wherein the liquid crystal display is displayed by a fieldsequential color system.